Hydraulic controls for an automatic transmission

ABSTRACT

A system for controlling a transmission fluid circuit includes a lube circuit, a source of control pressure, a first valve for engaging and disengaging a control element whose engagement produces desired forward gears, and a control valve, responsive to control pressure, that alternately connects the lube circuit to a sump and disconnects fluid feed to the first valve, and disconnects the lube circuit from the sump and feeds fluid to the first valve.

This application claims priority to and the benefit of U.S. ProvisionalApplication Nos. 61/446,157 and 61/446,173, filed Feb. 24, 2011, thefull disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an automatic transmission for a motor vehiclethat includes planetary gearsets and clutches and brakes whose state ofengagement and disengagement determines speed ratios produced by thetransmission.

2. Description of the Prior Art

In a front wheel drive vehicle, the axial space available for thetransmission is limited by the width of the engine compartment and thelength of the engine. In addition, the trend to increase the number ofratios available generally increases the number of components required.For these reasons, it is desirable to position components concentricallyin order to minimize axial length. The ability to position componentsconcentrically is limited, however, by the need to connect particularcomponents mutually and to the transmission case.

Furthermore, it is desirable for the output element to be located nearthe center of the vehicle, which corresponds to the input end of thegear box. An output element located toward the outside of the vehiclemay require additional support structure and add length on the transferaxis. With some kinematic arrangements, however, the need to connectcertain elements to the transmission case requires that the outputelement be so located.

An automatic transmission conventionally includes a manual valve, whichis moved by a cable in response to manual movement of the gear selectorto the selected range position. Shift-by-wire and range-by-wire selectorsystems usually have no manual valve, thereby requiring some other meansto protect against energizing a solenoid or engaging a gear that isother than the solenoid or gear corresponding to the selected range.

Generally the lube flow rate is set at a rate required to maximize theservice life of the clutches, brakes, gears and bearings due to amaximum torque condition. This flow rate is usually greater than thatrequired for normal driving conditions.

A need exists for a device that provides both a lube path, in whichlubricant flows to cool and lubricate the clutches, brakes, gears andbearings of the transmission and a parallel path to the sump.

SUMMARY OF THE INVENTION

A system for controlling a transmission fluid circuit includes a lubecircuit, a source of control pressure, a first valve for engaging anddisengaging a control element whose engagement produces desired forwardgears, and a control valve, responsive to control pressure, thatalternately connects the lube circuit to a sump and disconnects fluidfeed to the first valve, and disconnects the lube circuit from the sumpand feeds fluid to the first valve.

The automatic transmission control system includes no manual valve, yetthe range-by-wire selector system of the transmission protects againstenergizing a solenoid or engaging a gear that is other than the solenoidor gear corresponding to the selected range.

Due to the use of a OWC for first gear, only the ACL needs to be appliedto engage first gear, without a manual valve. If this clutchinadvertently applies, first gear will engage, even outside of thedriver selection of Drive. In the event of a failure of the ACL, thecontrol valve will go to the OFF condition and the cut-off valvedisconnects line pressure from the clutch whose engagement is required.

The cut-off valve provides both a lube path in which lubricant flows tocool and lubricate the clutches, brakes, gears and bearings and aparallel path to the sump, thereby providing maximum lube flow when amaximum torque condition occurs.

The scope of applicability of the preferred embodiment will becomeapparent from the following detailed description, claims and drawings.It should be understood, that the description and specific examples,although indicating preferred embodiments of the invention, are given byway of illustration only. Various changes and modifications to thedescribed embodiments and examples will become apparent to those skilledin the art.

DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood by reference to thefollowing description, taken with the accompanying drawings, in which:

FIG. 1 is a cross sectional side view of a multiple speed automatictransaxle;

FIG. 2 is cross sectional side view of the transaxle showing the frontand middle cylinder assemblies;

FIG. 3 is a side perspective view showing sleeves that are fitted on thefront support and middle cylinder assembly, respectively;

FIG. 4 is a view cross sectional side view of the transfer gears andshaft near the output of the transaxle of FIG. 1;

FIG. 5 is a side view showing a motor mounted within valve body andabove the elevation of the oil level in the valve body;

FIG. 6 is a perspective view of the motor secured to a separator plateon the valve body;

FIG. 7 is a perspective view showing the outer valve body, inner valvebody, and the motor mounted on the inner valve body;

FIG. 8 is a schematic diagram of a hydraulic control circuit for thetransmission; and

FIG. 9 is a table showing the applied and unapplied states of theclutches, brakes of the transmission and the solenoids of the controlcircuit of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, FIG. 1 illustrates gearing, clutches,brakes, shafts, fluid passages, and other components of a multiple-speedautomatic transaxle arranged substantially concentrically about an axis11.

A torque converter includes an impeller driven by an engine, a turbinehydrokinetically coupled to the impeller, and a stator between theimpeller and turbine. A transmission input shaft 20 is secured by aspline connection 21 to the turbine. The stator is secured by a splineconnection 22 to a front support 24, which is secured against rotationto a transmission case 26.

A double pinion, speed reduction planetary gearset 28 includes a sungear 30, secured by a spline connection 31 to input shaft 20; a carrier32, secured by a spline connection 33 to the front support 24; a ringgear 34, secured by a spline connection 35 to a front cylinder assembly36; a first set of planet pinions 38 supported on carrier 32 and meshingwith sun gear 30; and a second set of planet pinions 40, supported oncarrier 32 and meshing with ring gear 34 and the first pinions 38. Ringgear 34 rotates in the same direction as input shaft 20 but at a reducedspeed.

Rear gearset 46 and middle gearset 48 are simple planetary gearsets.Gearset 46 includes a set of planet pinion 50 supported for rotation oncarrier 52 and meshing with both sun gear 54 and ring gear 56. Gearset48 includes a set of planet pinions 58 supported for rotation on carrier60 and meshing with both sun gear 62 and ring gear 64. Sun gear 54 issplined to a shaft that is splined to a shell 66, on which shaft sungear 62 is formed, thereby securing the sun gears 54, 62 mutually and tothe shell 66. Carrier 52 is fixed to a shell 68. Carrier 60 and ringgear 56 are fixed to each other and to output pinion 70 through a shell72. Ring gear 64 is fixed to shell 74.

Front cylinder assembly 36, which is fixed to ring gear 34, actuatesclutches 76, 80. Plates for clutch 76 includes plates splined to frontcylinder assembly 36 alternating with plates splined to shell 74. Whenhydraulic pressure is applied to piston 78, the plates are forcedtogether and torque is transmitted between ring gears 34 and 64. Whenthe hydraulic pressure is released, ring gears 34 and 64 may rotate atdifferent speeds with low parasitic drag. Similarly, plates for clutch80 include plates splined to front cylinder assembly 36 alternating withplates splined to shell 66. When hydraulic pressure is applied to piston82, torque is transmitted between ring gear 34 and sun gears 54, 62.Pressurized fluid is routed from a control body 84, through frontsupport 24, into front cylinder assembly 36 between rotating seals.

Middle cylinder assembly 86, which includes carrier 32, actuates brake88. Plates for brake 88 include plates splined to carrier 32 alternatingwith plates splined to shell 66. When hydraulic pressure is applied topiston 90, the brake holds sun gears 54, 62 against rotation.Pressurized fluid is routed from the control body 84, through case 26 tofront support 24, between planet pinions 38, 40, into middle cylinderassembly 86. Due to the location of clutch pack 88, output element 70 islocated in the more favorable position near the front of the gear box.

Rear cylinder assembly 92 is secured by a spline connection 93 fixed toinput shaft 20. When hydraulic pressure is applied to piston 94, theplates of clutch 96 transmit torque between input shaft 20 and carrier52. Similarly, when hydraulic pressure is applied to piston 98, theplates of clutch 100 transmit torque between input shaft 20 and sungears 54, 62. Pressurized fluid is routed from the control body 84,through case 26 and cover 111 into rear cylinder assembly 92.

When hydraulic pressure is applied to piston 102, brake 104 holdscarrier 52 and shell 68 against rotation. A one-way brake 106 passivelyprevents carrier 52 and shell 68 from rotating in the negativedirection, but allows them to rotate in the forward direction. One-waybrake 106 may optionally be omitted and its function performed byactively controlling brake 104.

The D brake 104 is used only as a latching device not as a dynamicbrake. To minimize parasitic viscous drag loss produced in brake 104 itis desired that excess oil not be present in the brake. Therefore, anoil dam formed by an oil seal 103 between the piston 94 of E clutch 96and the inner race 107 of one-way brake 106 is provided to limit orprevent oil from entering the D brake 104. The inner radial end ofreturn spring 108 continually contacts the piston 102 that actuatesbrake 104. The outer radial end of return spring 108 continuallycontacts a fixed structure, so that the spring flexes as the piston 102moves in the cylinder of the D brake 104. In this way, return spring 108also participates in the oil dam by limiting or preventing radial flowof oil into the D brake 104 caused by centrifugal force.

This arrangement permits brake 88 and clutches 76, 80 to be mutuallyconcentric, located at an axial plane, and located radially outward fromthe planetary gearsets 28, 46, 48 such that they do not add to the axiallength of the gearbox. Similarly, clutches 96, 100 and brake 104 aremutually concentric and located radially outward from the planetarygearing 28, 46, 48. Clutches 76, 80, 96, 100 and brakes 88, 104, 106comprise the control elements.

As FIGS. 2A, 2B illustrate, the front cylinder assembly 36 is supportedfor rotation on the fixed front support 24 and carrier 34. The frontcylinder assembly 36 is formed with clutch actuation fluid passages,each passage communicating with one of the cylinders 114, 116 formed inthe front cylinder assembly 36. Cylinder 114 contains piston 78;cylinder 116 contains piston 82. One of the fluid passages in frontcylinder assembly 36 is represented in FIG. 2 by interconnected passagelengths 109, 110, 111, 112, through which cylinder 116 communicates witha source of clutch control hydraulic pressure. Another of the fluidpassages in front cylinder assembly 36, which is similar to passagelengths 109, 110, 111, 112 but spaced angularly about axis 11 frompassage lengths 109, 110, 111, 112, communicates a source of clutchcontrol hydraulic pressure to cylinder 114. Passage lengths 109 aremachined in the surface at the inside diameter of the front cylinderassembly 36.

The front cylinder assembly 36 is also formed with a balance volumesupply passage, similar to, but spaced angularly about axis 11 frompassage lengths 109, 110, 111, 112. The balance volume supply passagecommunicates with balance volumes 120, 122. As shown in FIG. 2A, thebalance volume supply passage includes an axial passage length 124,which communicates with a source of balance volume supply fluid andpressure, and a radial passage length 126, through which fluid flowsinto the balance volumes 120, 122 from passage 124. Passage 124 may be asingle drilled hole extending along a longitudinal axis and locatedbetween the two clutch balance areas of the A clutch and B clutch.Passage 124 carries fluid to cross drilled holes 126, which communicatewith the balance volumes 120, 122.

Coiled compression springs 128, 130, each located in a respectivebalance dam 120, 122, urge the respective piston 78, 82 to the positionshown in FIG. 2. Ring gear 34 is secured to front cylinder assembly 36by a spline connection 132.

Middle cylinder assembly 86 includes carrier 32, which is grounded onthe front support 24. Carrier 32 includes first and second plates 134,135 and pinion shafts secured to the plates, one pinion shaft supportingpinions 38, and the other pinion shaft supporting pinions 40. Plate 135is formed with a cylinder 140 containing a brake piston 90.

A source of brake actuating hydraulic pressure communicates withcylinder 140 through a series on interconnected passage lengths 142, 143and a horizontal passage length that extends axially from passage 143,through a web of carrier 32, between the sets of planet pinions 38, 40,to cylinder 140. These brake feed passages are formed in carrier 32.When actuating pressure is applied to cylinder 140, piston 90 forces theplates of brake 88 into mutual frictional contact, thereby holding sungears 54, 62 and shell 66 against rotation. A Belleville spring 146returns piston 90 to the position shown in FIG. 2, when actuatingpressure is vented from cylinder 140.

The front support 24 is formed with passages, preferably spaced mutuallyabout axis 11. These passages in front support 24 are represented in theFIGS. 1 and 2 by passage lengths 150, 151, 152, through which hydraulicfluid is supplied to clutch servo cylinders 114, 116, brake servocylinder 140, and balance dams 120, 122. A passage of each of the frontsupport passages communicates hydraulic fluid and pressure to cylinders114, 116 and balance dams 120, 122 of the front cylinder assembly 36through the fluid passages 109, 110, 111, 112, 113, 124 formed in thefront cylinder assembly 36. Another passage of each of the front supportpassages communicates hydraulic fluid and pressure to cylinder 140 ofthe middle cylinder assembly 86 through the fluid passages 142, 143 incarrier 32.

The front support 24 includes a bearing support shoulder 154, whichextends axially and over an axial extension 156 of the front cylinderassembly 36. A bushing 158 and bearing 160 provide for rotation of thefront cylinder assembly 36 relative to the front support 24. Thisarrangement of the front support 24, its bearing support shoulder 154,and front cylinder assembly 36, however, prevents radial access requiredto machine a passage or passages that would connect first passage 152 infront support 24 to the second passage 109 in the front cylinderassembly 36. To overcome this problem and provide hydraulic continuitybetween passage lengths 109, 152, first passage 152 is formed with anopening that extends along a length of first passage 152, parallel toaxis 11, and through an outer wall of the front support 24. The openingfaces radially outward toward second passage 109. Similarly, secondpassage 109 is formed with a second opening that extends along a lengthof second passage 109, parallel to axis 11, and through an inner wall ofthe front cylinder assembly 36. The second opening faces radially inwardtoward first passage 152.

A first sleeve 162 is inserted axially with a press fit over a surfaceat an outer diameter of the front support 24, thereby covering theopening at the outer surface of passage length 152. Sleeve 162 is formedwith radial passages 164, 165, which extend through the thickness of thesleeve 162. Seals 176, located at each side of the passages 164, 165prevent leakage of fluid from the passages.

A second sleeve 170 is inserted axially with a press fit over the secondopening at the inside diameter of the front cylinder assembly 36,thereby covering and enclosing the length of the second opening in thesecond passage 109. Sleeve 170 is formed with radial openings, two ofwhich are represented in FIG. 2 by openings 172, 174, aligned with theradial passages 164, 165 formed in the first sleeve 162.

Sleeves 164 and 170 provides hydraulic continuity from the source offluid pressure carried in the passages of the front support 24 to thebalance dams 120, 122 and the servo cylinders 114, 116, 140, throughwhich clutches 76, 80 and brake 88 are actuated.

Sleeves 162, 170 also provide access that enables machining of the firstand second passages 152, 109 in the surface at the outside diameter offront support 24 and in the surface at the inside diameter of the frontcylinder assembly 36. FIG. 3 shows sleeves 162, 170 and three seals 176,which are fitted in recesses on sleeve 162 between each of its radialpassages 164, 165.

As FIG. 4 shows output pinion 70 meshes with a transfer gear 180, whichis formed integrally with transfer pinion 182 on a transfer wheel 184. Atransfer shaft 186, is secured at one end by a pinned connection 188 toa non-rotating housing component 190, and at the opposite end is seatedin a recess 192 formed in a non-rotating torque converter housingcomponent 194. Ball bearing 198 supports transfer wheel 184 on thetorque converter housing 194. Housing components 190, 194 comprise areaction component and may be formed integrally or preferably asseparate components.

Ball bearing 198 is supported radially by being seated on a surface 196of the torque converter housing 194. A shoulder 199 on torque converterhousing 194 contacts the right-hand axial surface of the inner race ofbearing 198, the second surface of bearing 198. A snap ring 200 contactsthe right-hand axial third surface 201 of the outer race of bearing 198.Shoulder 199 and snap ring 200 limit rightward axial movement of bearing198.

A shoulder 202 formed on gear wheel 184 contacts the left-hand axialfirst surface of the outer race of bearing 198. A thrust washer 204contacts a left-hand axial fourth surface 205 of the inner race ofbearing 198. The thrust washer 204 contacts a shoulder 206 formed ontransfer shaft 186. Shoulders 202 and 206 limit leftward axial movementof bearing 198

The ring gear 210 of a differential mechanism 212 meshes with transferpinion 182 and is supported for rotation by bearings 214, 216 on housing190, 194. Rotating power transmitted to output pinion 70 is transmittedthrough transfer gears 180, 182 and ring gear 210 to the input ofdifferential, which drives a set of vehicle wheels aligned with axis220.

A roller bearing 222 supports transfer wheel 184 on transfer shaft 186.The thickness of a washer 224, fitted in a recess 226 of housing 190, isselected to ensure contact between thrust washer 204 and the inner raceof bearing 198.

The output pinion 70 and transfer gears 180, 182 have helical gearteeth, which produce thrust force components in the axial directionparallel to axis 220 and in the radial direction, normal to the plane ofFIG. 4. A thrust force in the right-hand direction transmitted to thetransfer gear wheel 184 is reacted by the torque converter housing 194due to its contact at shoulder 199 with bearing 198. A thrust force inthe left-hand direction transmitted to the transfer gear wheel 184 isreacted by the housing 190 due to contact between snap ring 200 andbearing 198, contact between bearing 198 and thrust washer 204, contactbetween the thrust washer and transfer shaft 186, and contact betweenshaft 186, washer 224 and housing 190.

As shown in FIG. 1A, the D brake 104 includes a first set of thin discs230 secured to the outer race 232 of one-way brake 106 by a splineconnection, which permits the discs 230 to move axially and preventsthem from rotating relative to the race 232, which is fixed to thetransmission case or end cover against rotation.

Similarly, the D brake 104 includes a second set of thin discs 234secured to the inner race 107 of one-way brake 106 by a splineconnection, which permits the discs 234 to move axially and preventsthem from rotating relative to the inner race 107. Inner race 107 isfixed to the carrier 68 of gearset 46, such that they rotate together asa unit at the same speed. Preferably the outer and inner races 232, 107of one-way brake 106 are formed of a ferrous alloy of sintered powderedmetal, and discs 230, 234 are of steel. Preferably the one-way brake 106is a rocker one-way brake of the type having a pivoting rockers, eachrocker retained is a pocket and actuated by centrifugal force and acompression spring, as described in U.S. Pat. Nos. 7,448,481 and7,451,862.

The reaction spline for the D clutch 104 is preferably not formed in thealuminum case or end cover because of high local stresses caused by thethin discs 232, 234 used to reduce parasitic loss. The D clutch reactionsplines are formed as an integral part of the raceways of the one-waybrake 106. The brake 106 is then splined to the transmission case.

FIG. 5 is a side view showing an electric motor 290, preferably abrushless motor, mounted within an inner valve body 292 and above theelevation 294 of the oil level in the valve body 292, such that themotor is not submerged in the oil. The rotor 296 of a hydraulic pump 298runs against a separator plate 300. No seal is required between themotor 290 and pump 298. Due to its elevation the motor 290 is vented toatmosphere, thereby improving the operating efficiency of theelectrically driven pump, sometimes called an E-pump. The inlet of pump298 is connected to a source of filtered automatic transmission fluid(ATF), i.e., oil.

FIG. 6 is a perspective view of the motor 290 and pump 298 securedthrough the separator plate 300 to the valve body 292.

FIG. 7 is a perspective view showing an outer valve body 302, whichcontains solenoids, located adjacent the inner valve body 292, whichcontains valves that are actuated by the solenoids to control operationof the transmission.

Referring now to FIG. 8, the hydraulic circuit includes a cut-off lubecontrol valve 310; a SS1 solenoid-operated valve 312, which responds tosolenoid feed pressure in line 313; a source cooled clutch feed fluid314 connected to an oil cooler 316; a source of line pressure 317produced by an engine-driven pump 326; an lube line 324 connecting valve310 to an elevated clutch vent 319 at an oil sump; a line 320 that feedsoil to a clutch, such as A clutch 78; and a line 322 carrying pressurefrom valve 312 to valve 310.

Regulated line pressure LP is carried in line 317. Output from pump 326is supplied to a main oil pump valve 301, which regulates line pressurein response to a line pressure control signal LPC carried in line 302 tovalve 301 from a solenoid-operated LPC valve 303. Solenoid pressure SFis carried in line 313 from a source of solenoid pressure, i.e., theoutput a variable displacement solenoid—actuated valve, to the linepressure control solenoid valve 303 and to SS1 valve 312.

When pressure in line 322 from SS1 valve 312 is high, the spool of valve310 moves against the force of its compression spring to the left-handend of its valve chamber, thereby connecting line 317 from line 320,which carries pressure to A clutch 78. Clutch feed pressure is carriedin lines 317 to the six control element, i.e., the clutches and brakesfrom a source of clutch feed pressure. Line 314 carries ATF to the lubecircuit 324, which supplies the balance dams 120, 122, and balance damsin clutches 96 and 100.

When pressure in line 322 from valve 312 is low, valve 310 shuttles tothe right-hand end of the valve chamber, thereby connecting line 314 andline 318. An orifice 419 can be used to control the flow rate in line318 to the sump 331 from valve 310.

Generally the lube flow rate is set at a rate required to maximize theservice life of the clutches, brakes, gears and bearings due to amaximum torque condition. This flow rate, however, is greater than thatrequired for normal driving conditions. Valve 310 provides both a lubepath, in which lubricant can flow to cool and lubricate the clutches,brakes, gears and bearings and a parallel path to the sump 331.

The hydraulic circuit supplies filtered ATF drawn from sump 331 to anauxiliary pump 298, driven by brushless motor 290. When the vehicleincludes an automated start-stop function, which automatically stops theengine at a traffic light or when no torque is demanded andautomatically restarts the engine when torque is demanded, the auxiliarypump valve 330 is supplied through pump 298 and line 332 with ATF fromsump 331.

In operation, when regulated line pressure in line 317 is high, valve330 shuttles to the left-hand end of its chamber, thereby connectingfluid in line 332 from the E-pump 298 to line 334, oil cooler 316, line314 and lube circuit 324.

When line pressure in line 318 is low, the spool of valve 330 moves tothe right-hand end of its chamber, thereby disconnecting the outlet ofpump 298 from line 334, cooler 316 and lube circuit 313 and connectingcircuit 332 to line pressure circuit 317.

In this way, when the engine is running, the engine-driven hydraulicpump 326 is running, and regulated line pressure to be high, AFT fromE-pump 298 increases the ATF flow rate to the cooler 316, therebyhelping to reduce the temperature of ATF in the hydraulic circuit, andto lube circuit 324, thereby increasing the flow of lubricant thatlubricates the transmission. This operation of the E-pump 298 and motor290 can occur, without limitation, when the vehicle is towing a heavyload, or immediately following a high engine torque condition, orwhenever ATF temperature is high, and combination of these conditions.

An automatic transmission conventionally includes a manual valve, whichis moved by a cable in response to manual movement of the gear selectorto the selected range position. Shift-by-wire and range-by-wire selectorsystems usually have no manual valve. The range-by-wire system of thistransmission therefore requires some means to protect against energizinga solenoid or engaging a gear that is other than the solenoid or gearcorresponding to the selected range.

When the spool of valve 310 moves to the right-hand end of the chamberdue to low pressure from SS1 valve 312 in line 322, line pressure 317entering at the inlet port of valve 310 is blocked by valve 310, therebypreventing line pressure from being feed through PC1F line 320 to the Aclutch 76, and directing clutch feed pressure in CF line 314 through theelevated clutch vent 319 to sump 331. Due to low pressure in line 322,the A clutch 78 is disengaged because no actuating pressure is feed toclutch 78. As indicated in the clutch/solenoid application chart of FIG.9, the A clutch 78 must be engaged to produce the first through fifthforward gears. Pressure in line 322 is low when the range-by wire systemselects a range other than the gears one through five.

When valve 310 shuttles to the left-hand end of the chamber due to highpressure from SS1 valve 312 in line 322, line pressure in line 317 atthe inlet port of valve 310 is connected through valve 310 to PC1F line320, thereby connecting line pressure to valve 340, which feeds shiftcontrol pressure to the A clutch 78 subject to control of PC1 solenoid342. Also CF line 314 is disconnected from sump 331 through line 318 andvent 319. This action allows the A clutch 76 to engage, thereby enablingeach of the first five lowest forward gears to engage as required andallowing a high rate oil flow to the lube circuit 324, due to valve 310disconnecting line 314 from line 318 to sump 331. Pressure in line 322is high when the range-by wire system selects the DRIVE range with gearsone through five.

Therefore, even without a manual valve and while pressure in SS1 line322 is low, the first through fifth gear cannot be produced, but reversedrive and sixth, seventh and eighth forward gears can be produced,thereby permitting the vehicle to be driven. In the event of a failureof the ACL in the ON condition in conjunction with the OWC, the resultwould be first gear in Neutral and Park, but the cut-off valve 310 candisconnect line pressure in LP line 317 from PC1F line 320 to the Aclutch 78 through ACL line 344, allowing the A clutch to disengage andproducing no first gear.

In accordance with the provisions of the patent statutes, the preferredembodiment has been described. However, it should be noted that thealternate embodiments can be practiced otherwise than as specificallyillustrated and described.

The invention claimed is:
 1. A system for controlling a transmissionfluid circuit, comprising: a lube circuit; a source of control pressure;a first valve for engaging and disengaging a control element whoseengagement produces desired forward gears; a control valve, responsiveto control pressure, that alternately connects the lube circuit to asump and disconnects fluid feed to the first valve, and disconnects thelube circuit from the sump and feeds fluid to the first valve.
 2. Thesystem of claim 1, wherein: the lube circuit includes an oil cooler; andthe sump is arranged in parallel with the lube circuit between the sumpand a line that carries fluid to the lube circuit and the control valve.3. The system of claim 1, wherein the source of control pressure is asolenoid-operated valve that produces high and low control pressure, thesystem connecting the lube circuit to the sump and disconnecting fluidfeed to the first valve when control pressure is relatively low, anddisconnecting the lube circuit from the sump and feeding fluid to thefirst valve when control pressure is relatively high.
 4. The system ofclaim 1, further comprising a source of regulated line pressure thatprovides the fluid feed to the first valve.
 5. The system of claim 4,wherein the source of regulated line pressure further comprises: a pumpdriven by an engine; a solenoid-actuated line pressure control valve;and a regulator valve communicating with an outlet of the pump outputand the line pressure control valve for producing regulated linepressure in response to a pressure signal from the line pressure controlvalve.
 6. The system of claim 1, wherein the control valve includes: achamber; a spool moving in the chamber for opening and closing ports; aspring urging the spool to a first position; a port connected to thecontrol valve for opposing the spring; a second port connected to asource of line pressure; a third port connected to the lube circuit; afourth port connected to the sump; and a fifth port connected to thefirst valve.
 7. The system of claim 1, further comprising an orificethat controls a flow rate of fluid to the sump.
 8. A system forcontrolling a transmission fluid circuit, comprising: a source ofcontrol pressure; a first valve for engaging and disengaging a controlelement, whose engagement produces desired gears; a control valve,responsive to control pressure, that alternately disconnects fluid feedto the first valve, and feeds fluid to the first valve; wherein thesource of control pressure is a solenoid-operated valve that produceshigh and low control pressure, the system disconnecting fluid feed tothe first valve when control pressure is relatively low, and feedingfluid to the first valve when control pressure is relatively high. 9.The system of claim 8, further comprising: a lube circuit; and thecontrol valve, responsive to control pressure, that connects the lubecircuit to a sump when the control valve disconnects fluid feed to thefirst valve, and disconnects the lube circuit from the sump when thecontrol valve feeds fluid to the first valve.
 10. The system of claim 9,wherein: the lube circuit includes an oil cooler; and the sump isarranged in parallel with the lube circuit between the sump and a linethat carries fluid to the lube circuit and the control valve.
 11. Thesystem of claim 8, further comprising a source of regulated linepressure that provides the fluid feed to the first valve.
 12. The systemof claim 11, wherein the source of regulated line pressure furthercomprises: a pump driven by an engine; a solenoid-actuated line pressurecontrol valve; and a regulator valve communicating with an outlet of thepump output and the line pressure control valve for producing regulatedline pressure in response to a pressure signal from the line pressurecontrol valve.
 13. The system of claim 8, wherein the control valveincludes: a chamber; a spool moving in the chamber for opening andclosing ports; a spring urging the spool to a first position; a portconnected to the control valve for opposing the spring; a second portconnected to a source of line pressure; a third port connected to thefirst valve.
 14. A system for controlling a transmission fluid circuit,comprising: a source of control pressure whose magnitude that varieswith whether a transmission range, selected other than by actuating amanual valve, requires that a control element be disengaged and engaged;a first valve for changing a state of the control element; a controlvalve, responsive to control pressure, that alternately disconnectsfluid feed to the first valve, and feeds fluid to the first valve;wherein the source of control pressure is a solenoid-operated valve thatproduces high and low control pressure, the system disconnecting fluidfeed to the first valve when control pressure is relatively low, andfeeding fluid to the first valve when control pressure is relativelyhigh.
 15. The system of claim 14, further comprising: a lube circuit;and the control valve, responsive to control pressure, that connects thelube circuit to a sump when the control valve disconnects fluid feed tothe first valve, and disconnects the lube circuit from the sump when thecontrol valve feeds fluid to the first valve.
 16. The system of claim14, further comprising a source of regulated line pressure that providesthe fluid feed to the first valve.
 17. The system of claim 16, whereinthe source of regulated line pressure further comprises: a pump drivenby an engine; a solenoid-actuated line pressure control valve; and aregulator valve communicating with an outlet of the pump output and theline pressure control valve for producing regulated line pressure inresponse to a pressure signal from the line pressure control valve. 18.The system of claim 14, wherein the control valve includes: a chamber; aspool moving in the chamber for opening and closing ports; a springurging the spool to a first position; a port connected to the controlvalve for opposing the spring; a second port connected to a source ofline pressure; a third port connected to the first valve.
 19. A systemfor controlling a transmission fluid circuit, comprising: a source ofcontrol pressure whose magnitude that varies with whether a transmissionrange, selected other than by actuating a manual valve, requires that acontrol element be disengaged and engaged; a first valve for changing astate of the control element; a control valve, responsive to controlpressure, that alternately disconnects fluid feed to the first valve,and feeds fluid to the first valve; a lube circuit; and the controlvalve, responsive to control pressure, configured to connect the lubecircuit to a sump when the control valve disconnects fluid feed to thefirst valve, and disconnects the lube circuit from the sump when thecontrol valve feeds fluid to the first valve.